1. Field Of The Invention
The present invention relates to computers and to disk drive storage systems for computers. More particularly, the present invention relates to apparatus and methods for preventing data corruption on a disk resulting from mechanical shock experienced by the disk drive during the write process to the disk.
2. The Prior Art
Historically, disk drives started as very large immovable devices, weighing over 2000 pounds, and having disk diameters ranging from 2 to 4 feet. Disk sizes quickly evolved to 14 inches and smaller. As development continues, disk drives are continually shrinking in size to accommodate new applications. As disk diameters become smaller, the issue of damage from mechanical shock begins to become a significant factor. As continuing evolution shrinks disk diameters below two inches, mechanical shock becomes a major concern for the first time.
The present concern over the issue of potential damage from mechanical shock results from the development of the small disk drives which are designed to reside in small "laptop" and "notebook" portable computers. Larger disk drives (i.e., 5.25 inch and 3.5 inch) are generally mounted into larger computer systems housed in larger cases, usually residing on desk tops, or in even larger "tower" cases which are placed on the floor. In these environments, the 5.25 inch and 3.5 inch drives are quite safe from damage due to accidental mechanical shocks.
The smaller 2.5 inch drives are employed in lap-top computers, an environment in which they are much more likely to be bumped and jostled. A lap-top computer system weighs from about 5 to 15 pounds. This weight helps lower the peak g-force experienced by the hard disk drive inside the lap-top computer when it is subjected to most mechanical shocks which can be anticipated to occur in its operating environment.
A major market which appears to be developing for the 1.8 inch drives is the palm-top computer. The palm-top computers will be very small and will probably weigh only about 1 to 2 pounds, and can be moved very quickly compared to the lap-top units. Also, palm-top computers are more susceptible to being accidentally bumped, jarred, or even dropped during operation. Because of their low weight, the small disk drive in a palm-top computer can be subjected to a substantial amount of mechanical shock during normal operation of the computer.
There are some effects of mechanical shock which are unpreventable. The worst-case preventable condition, resulting from mechanical shocks, occurs when the drive is writing data to a disk. In this state, the head is positioned over the proper track to record the data. If the mechanical shock is severe enough to cause the head to move over an adjacent data track before the write current in the data head is turned off, the data in the adjacent track will be corrupted. This damaged data is not recoverable. Neither the computer nor disk drive controller know what data was damaged, when and how it was originally generated, and has no way to fix the damaged data. The user will not even know that the data has been corrupted until a read failure is experienced at some later time. It will be too late to reconstruct the corrupted data unless it has previously been backed up.